1. Field of the Invention
This invention relates to heat pipes for conducting heat away from electronic circuitry and, more particularly, to heat pipes which are particularly well adapted to airborne avionics and to the radar systems used therein.
2. Description of Related Art
As is well known, electronic circuitry often generates heat. For maximum efficiency and longevity, means are often provided to remove or reduce this heat.
Devices called heat pipes have been used for this purpose. Traditionally, heat pipes consist of a wick and fluid housed in a sealed chamber. One end is subjected to heat; the other to a cold wall. The liquid at the heated end boils, the vapor travels to the cold end and condenses, and the capillary action of the wick causes the condensed fluid at the cold end to travel back to the heated end for re-vaporization.
The vapor pressure, unfortunately, is often quite high. For example, the internal working pressure of ammonia at 70 degrees centigrade is approximately 900 pounds per square inch. The chamber, therefore, must be quite strong in order to contain this pressure. Aluminum and copper, for example, typically must have a wall thickness of approximately 0.035 inches. Stainless steel typically must have a wall thickness of approximately 0.023 inches.
These great thicknesses, in turn, add substantial weight to the heat pipe. In many applications, such as airborne avionics, this weight is highly undesirable.
The materials which are typically used for the outer cylinder of the heat pipes, moreover, conduct electricity. As a consequence, interfaces are usually required to electrically isolate the heat pipe from the circuitry. This adds further bulk and weight to the system and reduces heat transfer efficiency.